Electroluminescent devices represent an important current and future product in the electronic display industry. Such devices may be constructed in a configuration comprising an electroluminescent material positioned in electronic communication with electron-injection and hole-injection electrodes. When a voltage is applied to the electrodes, holes and electrons are injected into the electroluminescent material from the hole-injection and electron-injection electrodes, respectively. Once the holes and electrons are combined in the electroluminescent material, light is emitted.
OLED is an acronym for an organic light-emitting diode in which an organic emissive electroluminescent (EL) material may be applied as a layer, the layer emitting light in response to an electric potential or current. Two major areas of research in OLED are solid state lighting and display application. In recent years, devices containing organic light emitting diodes (OLED) have been proposed that use organic compounds such as perylenes, thiazole derivatives, quinacridone derivatives, rubrenes, benzophenone derivatives, and coumarin derivatives. However, conventional fluorescent organic compounds typically exhibit a low luminous efficiency. Exciton production efficiency is limited to about 25% due to the deactivation of triplet excitons. When used in an organic EL element, the luminescent efficiency is at most about 5%.
High color purity and long operational lifetimes for deep blue display applications have been problematic in traditional OLED devices for several decades. Therefore, development of efficient and operation stable blue OLED would dramatically impact on the success of display and light applications.
Recently, devices exhibiting TADF have demonstrated highly efficient EL performance, exceeding over 19% of external quantum efficiency. One main strategy in material design for TADF involves incorporating donor and acceptor units together in an orthogonal fashion to separate highest occupied molecular orbitals (HOMO) from lowest unoccupied molecular orbitals (LUMO), thereby leading to small orbital overlap between HOMO and LUMO. This results in a small energy gap between singlets and triplets, allowing a reverse intersystem crossing (RISC) to occur to provide a highly efficient OLED.
It is known that certain porphyrin-based metal complex may be used as a fluorescent organic compound as a light-emitting material for the organic EL element. In such a case, the porphyrin-based metal complex may exhibit TADF. Additional TADF compounds are known in the art as well.
Nevertheless, opportunities exist to provide alternatives to known TADF compounds and to improve known electroluminescent display technologies.